The Development of the Alligator 313 
plate, along whose medial side it courses. The 
ventral nerve root is plainly seen; the dorsal root, 
in this section, less plainly. The amnion (a) and 
abdominal wall are, as in the preceding figure, 
torn in the region of the ventricle. 
Figure 17e is a short distance posterior to the 
figure just described. The liver is cut through its 
middle region and forms a large, darkly staining, 
reticular mass on the left side of the figure. The 
digestive tract is seen at two places to the right of 
the liver; the smaller and more ventral of these 
openings (7) may be called the intestine, while 
the larger is evidently the stomach (z’). The 
body wall is here unfused and becomes suddenly 
thinner as it passes upward into the amnion (a). 
The Wolffian tubules (wt) form a very conspicuous 
mass on either side of the mesentery, in close con- 
nection with the posterior cardinal veins (fc). 
In the mesoblast between the dorsal aorta (ao) 
and the notochord are two small, irregular, darkly 
stained masses (sy). These are shown in the 
preceding two figures, but were not mentioned 
in the description. They may be traced through 
a great part of the length of the embryo back of 
the head region; at intervals corresponding in 
length to the distance between the spinal ganglia 
they are enlarged, while between these enlarge- 
ments they are very small in cross-section. At 
certain points a small blood-vessel is given off by 
the dorsal aorta to the immediate neighborhood 
